Abstract

Tritium is an important natural tracer in the hydrological sciences. Measurements of the tritium activity of precipitation in the Adriatic-Pannonian region began in Vienna Hohe Warte in 1961, which is the longest continuously operating station in Central Europe. The dataset used in the present study is compiled of ~7500 monthly precipitation tritium activity values from 68 stations covering the period from Jan 1961 to Dec 2017. To maximize the spatiotemporal density of the data not only the Adriatic-Pannonian region, but the bordering areas were included in the analyses as well. Changes in the availability of tritium data from the different stations outlined three time horizons with a relatively high abundance of data, i.e. early 1980s (n≈15), late 2000s (n≈21) and the 2010s (n≈19). Two years were chosen from each period for investigation where the station densities reached their maxima. Variogram analysis was applied to the amount weighted annual averages of tritium activity. The results suggested a decrease in spatial representativity of the precipitation monitoring stations for the three time horizons (~500, ~400, ~300 km respectively), which might reflect the diminishing influence of broadly homogenous nthropogenic disturbance (i.e. global effect of bomb tests) on natural tritium levels of precipitation. However, this hypothesis needs further verification, primarily by including additional stations and archived data. Based on the preliminary evaluation at least 15 stations are required to derive a meaningful tritium isoscape for the Adriatic-Pannonian region. A further, almost trivial, requirement is that the stations should not be clustered instead well distributed over the region. As final products of the research, the annual precipitation tritium activities are mapped and presented as numerical data as well (1 km × 1 km grid) from the late 1970s to 2002 and after 2007 when the spatiotemporal data density was sufficient. The obtained product will provide a spatially more accurate reference for infiltration modelling, hydrological residence/transit time estimation and for the campaigns related to water resource protection. Last but not least, an accurate picture of the normal spatial distribution of precipitation 3H is of interest also due to the possible nuclear accidents. Acknowledgements: This work was supported by the National Research, Development and Innovation Office ; under Grant SNN118205 ; Slovenian Research Agency ARRS under Grants: N1-0054 and P1-0143, and the Ministry of Human Capacities under Grant NTP-NFTÖ-17-B-0028.

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